When playing sports, people can become dehydrated. Running to a bench or some other location to retrieve a drink of water is mot only time consuming but is not always possible, particularly if the person is a runner and gets far away from a drink location. Having a way to carry one's water or other beverage could save them time and energy while the person is participating in various activities.
Thus, it would be advantageous if there were a simple and secure means for carrying a bottle with water or some other beverage on the person so that the beverage would be with him/her and be available when needed.